1. Field of the Invention
The present invention relates to offshore drilling rigs and more particularly to the installation of a pipe string through an offshore drilling rig already in place to the sea floor.
2. Description of the Prior Art
Due to the nature and configuration of an offshore platform it is quite difficult to lower a pipe string or other such object through such a structure after its already in place. Such a structure is usually comprised of a series of support pipes which extend to and into the sea floor. At regular intervals there are located structural templates through which the support pipes extend. The result is that, particularly close to the surface, the unfilled gaps in such structural templates are quite small. Therefore, when it is found that an offshore rig requires additional cathodic protection, it is quite difficult to put in place additional anodes. Attempts to place and mount additional anodes have usually been made through the use of divers and/or submarines. This method has proved ineffective in deep water. When attempting to lower a pipe string or other such object from the top deck of the rig, it's quite difficult to place whatever is being lowered into the framework of the structure. This is because the top platform cantilevers well beyond the support structure at the point where the support structure meets the top platform. In the case of anodes, it is quite desirable to have them placed throughout the support structure and therefore in places which cannot possibly be reached by the use of cranes booming out from the top platform.